A transparent conductive film is used for various devices such as a touch panel, a solar battery, an electronic paper, and an image sensor. Materials generally used as a transparent conductive film include indium tin oxide (ITO). An ITO film is a conductive material having extremely high optical transmittance. However, in recent years, depending on application, conductivity equivalent to that of the ITO film and optical transmittance higher than that of the ITO film, or optical transmittance equivalent to that of the ITO film and conductivity higher than that of the ITO film have been demanded.
Materials attracting attention lately as alternatives to ITO include graphene. When a covalent bond between carbon atoms occurs due to a sp2 hybrid orbital, a network structure film in which six-membered rings (a five-membered ring or a seven-membered ring may be included in some cases) are spread all over a planer surface. This network structure film of carbon atoms is called graphene, and what is formed by laminating a large number of (typically, some hundreds of) graphenes is called graphite.
Graphene is obtained by, for example, affixing a Scotch tape (Scotch is a registered trademark of 3M) to graphite; exfoliating graphene by using adhesive strength of the tape; and transferring the graphene to a silicon wafer in which an SiO2 film is formed on a surface. Recently, graphene has been formed using CVD (Chemical Vapor Deposition), and graphene having excellent properties has been obtained (see Patent Literature 1).